Deepwater Horizon Oil Well Explosion
Fire boat response crews battle the blazing remnants of the offshore oil rig Deepwater Horizon, off Louisiana, on April 21, 2010. Reuters

The April 2010 accident on BP's Deepwater Horizon rig off the Louisiana coast has created a “bathtub ring” made of an oil-rich layer of water on the seabed in the Gulf of Mexico, according to a new study. The disaster is considered to be the largest accidental marine oil spill in the world and the largest environmental tragedy in U.S. history.

Scientists working on the study have described the path the oil followed to create a footprint on the ocean floor, and estimate that the oil spill has left about two million barrels of submerged oil in the ocean. The explosion, which reportedly killed 11 workers and injured 16 others, caused the Deepwater Horizon rig to burn and sink, resulting in a massive offshore oil spill in the Gulf of Mexico. The rig, known as a semi-submersible mobile offshore drilling unit, was located in the Macondo Prospect oil field about 40 miles from the coast.

“Our findings suggest that these deposits come from Macondo oil that was first suspended in the deep ocean and then settled to the sea floor without ever reaching the ocean surface,” David Valentine, a geochemistry professor at the University of California Santa Barbara, said in a statement. “The pattern is like a shadow of the tiny oil droplets that were initially trapped at ocean depths around 3,500 feet and pushed around by the deep currents. Some combination of chemistry, biology and physics ultimately caused those droplets to rain down another 1,000 feet to rest on the sea floor.”

As part of the study, published Monday in the journal Proceedings of the National Academy of Sciences, the scientists used data from the Natural Resource Damage Assessment process conducted by the National Oceanic and Atmospheric Administration to analyze more than 3,000 samples collected at 534 locations. They identified a 1,250-square-mile patch of the deep sea floor -- about the size of Rhode Island -- where 2 percent to 16 percent of the discharged oil was deposited.

The scientists also identified hotspots in close proximity to damaged deep-sea corals, supporting a previously disputed finding that these corals were damaged by the Deepwater Horizon spill. Florida State University researchers recently found that a certain kind of bacteria has been consuming some of the chemicals that were released when the oil flowed out into the ocean for 87 days.

“The evidence is becoming clear that oily particles were raining down around these deep sea corals, which provides a compelling explanation for the injury they suffered,” Valentine said in the statement. “The pattern of contamination we observe is fully consistent with the Deepwater Horizon event but not with natural seeps — the suggested alternative.”

According to scientists, the study examined only a specific area, and oil deposits could likely be found outside the study area. Meanwhile, BP, which has reportedly spent more than $14 billion cleaning up the spill, questioned the study's findings.

The study’s “authors failed to identify the source of the oil, leading them to grossly overstate the amount of residual Macondo oil on the sea floor and the geographic area in which it is found,” Jason Ryan, a BP spokesperson, told The Associated Press.